1. Field of the Invention
The present invention relates to an improvement in a saddle type vehicle provided with a secondary air supply system.
2. Description of Background Art
A saddle type vehicle is known wherein a secondary air supply system is provided for clarifying an exhaust gas by combustion of unburned components present in the exhaust gas. See, for example, Japanese Patent No. 3237285, FIGS. 1 and 2.
As shown in FIGS. 1 and 2 of Japanese Patent No. 3237285, in a saddle type motorcycle, a pair of main frames (16) (parenthesized numerals used herein are reference numerals used in Japanese Patent No. 3237285, the same shall apply hereinafter) extend rearwardly from a head pipe (15) with an engine (9) being suspended on the main frames (16). The secondary air supply system is disposed between the engine (9) and the main frames (16). The secondary air supply system is provided with reed valves (12, 12) which are each opened when a predetermined negative pressure is exerted thereon. The reed valves (12, 12) are disposed to be exposed to an exhaust passage of the engine (9).
The engine (9) mounted on the saddle type vehicle in Japanese Patent No. 3237285 is a two-cylinder engine in which two cylinders of the engine are arranged in a row along the transverse direction of the vehicle. In an engine different in cylinder layout from this type of engine, for example, in a so-called V-type engine in which a plurality of cylinders are arranged in a V-shaped configuration with a crankshaft at the vertex of the V shape, a preferable layout for the secondary air supply system may be different from that in the above-mentioned type.
It is desired to develop a technology that enables an efficient and compact layout of a secondary air supply system in a so-called V-type engine which includes a front-side cylinder or cylinders and a rear-side cylinder or cylinders.